Fabrication of advanced three dimensional semiconductor structures with complex surface topology and high packing density presents many technical challenges. As the critical dimension of devices and the pitch decreases, the aspect ratio of features increases. For example, this trend results in deep, but very narrow trenches on the surface of the workpiece. These trenches may be created using a technique known as reactive ion etch, or RIE. Trimming and forming the various trench liner materials may be performed using a technique known as directed reactive ion etching, DRIE. Precise angle control is used to selectively etch a specified portion of the walls of these trenches. Angular control of an ion beam may be obtained through the manipulation of electrical fields, which serve to focus the ions in a particular direction.
The etch rates of reactive ion etching may be enhanced by supplementing the charged ion beam with reactive neutrals. However, reactive neutrals are not controllable using electrical fields. Therefore, while the angle of the charged ion beam may be precisely controlled, the same is not true for reactive neutrals. As the angles used for DRIE decrease (i.e. become closer to perpendicular to the workpiece), the lack of angular control of the reactive neutrals becomes more pronounced. Reactive neutrals are defined as those radicals/atoms which are highly reactive with some of the materials on the workpiece, but not others. For example, under the correct process conditions, chlorine has a high reaction rate with TiN, but a very low reaction rate with SiO2. These reactive neutrals serve to etch portions of the workpiece, without affecting other parts. The inability to control the angle at which the reactive neutrals are directed toward the workpiece may compromise the speed of the etching process. In certain embodiments, the inability to control the angle at which the reactive neutrals are directed toward the workpiece may make it difficult to achieve the specified feature on the workpiece.
Thus, it would be beneficial if there was an apparatus which could control the angle at which reactive neutrals are directed toward a workpiece. Further, it would beneficial if the apparatus also controls the angle at which charged ions are directed toward the workpiece. Such an apparatus may be beneficial in certain applications, such as directed reactive ion etching.